How big is the container (dimensions)? And where in New England are you located (NE covers a lot of zones)?

Plants grown in containers will have less cold tolerance than the same plant in the ground. That's because the root system - the most cold sensitive part of the plant - is exposed on all sides to ambient air temps, which will be far colder than the ground soil and lacks the insulating mass that provides. That is also why it is recommended to not overwinter containerized plantings outdoors unless the plant is fully hardy to at least two zones lower than your own.

Montauk daisy also gets to be a big plant - 3'x3', sometimes larger. If it survives winter, will it fit?

Thanks. Dimensions 3 feet long - about 12 inches deep (down) and probably the same front to back. 12 inches. I am in RI - zone 6A - I know they get large and it won't stay in that box if it does. I am looking at a couple of years for that area. Thanks again.